When buying or selling a gemstone, knowing its authenticity is crucial. But how can you tell one gemstone from another? The answer lies in testing! Gemologists use a variety of equipment to examine gemstones, evaluating key traits such as structure, light refraction, and color variation. Each test reveals vital information, bringing you closer to identifying the gemstone. In this article, we’ll discuss how each tool works, its purpose, and how to use it.
How to Test Gemstone A Complete Guide
The two most important components of gemstone testing are knowledge and practice. You don’t need a Ph.D. in Gemology to learn how to identify gems; all you need is some information and practice.
1. Get Educated
The Gemological Institute of America (GIA) offers some of the most respected courses, especially its Gemstone Identification Lab course. Courses are available both in-person and online through their Distance Education program, with costs averaging around $250. While GIA sets the industry standard, there are also more affordable options. The International Gem Society (IGS) offers mini-courses on specific gemstones for around $25 each. And of course, you’ll find plenty of valuable information on the Chroma Gems & Co Blog.
2. Have a Reference Book
A gemstone reference book is one you’ll turn to time and time again. It’s an essential tool for any beginner. Here are three top recommendations:
- Gem Identification Made Simple by Antoinette Matlins
- Tables for Gemstone Identification by Roger Dedeyne and Ivo Quintens
- The Internal World of Gemstones by Eduard Josef Gübelin
Once you’ve got your course and reference materials ready, you’re all set to explore the tools!
Best Tools for Gemstone Testing
1. Loupe
The first step in gemstone identification is taking a closer look at the stone. The best tool for this is a loupe—a pocket-sized magnifier that helps you see intricate details. While you might think a magnifying glass could work, a loupe is much more portable, has a protective cover, and offers a sharper, more accurate image.
There are three main types of loupes:
- Singlet: A basic, single-lens magnifier, but it can produce slight image distortion.
- Doublet: Features two lenses for a sharper, more precise view.
- Triplet (Prismatic): The industry standard, with three lenses that offer the best possible clarity and color correction—essential for gemstone identification.
Loupes come in different magnification powers: 10x, 20x, and 30x. For most gemstone identification tasks, a 10x loupe is ideal. It provides enough magnification without sacrificing clarity.
To use a loupe, simply hold it up to your eye, bring the gemstone close to the lens, and move it around to view different facets. If you collect gemstones while traveling, you might also want to invest in a dark field loupe, which can highlight inclusions by displaying the gem’s color against a black background.
2. Refractometer
Once you’ve visually examined the stone, the next step is to measure its refractive index (RI) using a refractometer. The RI tells you how light bends as it passes through the stone. Every gemstone has a unique RI; for instance, sapphires and rubies (both corundum) have RIs between 1.76 and 1.77.
To use a refractometer, place the gemstone on a glass hemicylinder filled with refractometer fluid. When light hits the stone, a shadow line will appear on a calibrated scale. The number at the shadow line represents the stone’s refractive index.
3. Dichroscope
Have you ever tilted a gemstone and noticed it changing colors? This phenomenon, called pleochroism, can be examined with a dichroscope. Pleochroism occurs when a gemstone reflects different colors depending on the viewing angle.
The dichroscope shows two color blocks at the end of the tube. If the blocks are the same color, the gemstone is singly refractive (non-pleochroic). If the colors differ, it is doubly refractive, meaning it displays pleochroism.
There are two types of dichroscopes: calcite and polarizing. Calcite dichroscopes are preferred because they provide more accurate color readings, while polarizing dichroscopes may distort colors with a greenish tint.
Ready to Identify Gemstones?
Now that you’ve learned about the essential tools for gemstone identification, you’re ready to get started! Identifying gemstones requires patience and a combination of testing methods. With the right equipment, proper education, and plenty of practice, you’ll soon be able to test gemstones confidently at home. Start studying and using these gemstone testing tools, and you’ll quickly become a skilled gemstone handler!